The specific objectives of our research are to define the mode of action and structure-activity relationships for certain antitumor and antiviral agents and to explore the molecular basis for their interaction with macromolecules. The primary agents under investigation at the present time are the bleomycins, a family of structurally-related glycopeptide antibiotics which possess antimicrobial, antitumor and antiviral properties. Determining the mode of action of the bleomycins may be of value in establishing normal pathways of macromolecular synthesis as well as in correlating biochemical properties of drugs with therapeutic activity. Knowledge of the mode of action suggests new uses and may warn against unsuspected toxicities. Information gained from these studies may provide clues that will lead to the development of new chemotherapeutic agents.